This invention relates in general to a slip joint, such as is commonly used in a driveshaft assembly for transmitting rotational force or torque from an engine/transmission to an axle assembly in a vehicle drive train system. In particular, this invention relates to a pressure regulator assembly for use with such a slip joint that compresses a volume of lubricant disposed within a sealed lubricant chamber defined within the slip joint so as to maintain a positive pressure situation within the lubricant chamber and thus deter the entry of contaminants therein.
Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine/transmission assembly generates rotational power, and such rotational power is transferred from an output shaft of the engine/transmission assembly through a driveshaft assembly to an input shaft of an axle assembly so as to rotatably drive the wheels of the vehicle. To accomplish this, a typical driveshaft assembly includes a hollow cylindrical driveshaft tube having a pair of end fittings, such as a pair of tube yokes, secured to the front and rear ends thereof. The front end fitting forms a portion of a front universal joint that connects the output shaft of the engine/transmission assembly to the front end of the driveshaft tube. Similarly, the rear end fitting forms a portion of a rear universal joint that connects the rear end of the driveshaft tube to the input shaft of the axle assembly. The front and rear universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes of these three shafts.
Not only must a typical drive train system accommodate a limited amount of angular misalignment between the source of rotational power and the rotatably driven device, but it must also typically accommodate a limited amount of relative axial movement therebetween. For example, in most vehicles, a small amount of relative axial movement frequently occurs between the engine/transmission assembly and the axle assembly when the vehicle is operated. To address this, it is known to provide a slip joint in the driveshaft assembly. A slip joint includes first and second members that have respective structures formed thereon that cooperate with one another for concurrent rotational movement, while permitting a limited amount of axial movement to occur therebetween. A typical sliding spline type of slip joint includes male and female members having respective pluralities of splines formed thereon. The male member is generally cylindrical in shape and has a plurality of outwardly extending splines formed on the outer surface thereof. The male member may be formed integrally with or secured to one of the end fittings described above to form a slip yoke. The female member, on the other hand, is generally hollow and cylindrical in shape and has a plurality of inwardly extending splines formed on the inner surface thereof. The female member may be formed integrally with or secured to an end of the driveshaft tube described above. To assemble the slip joint, the male member is inserted within the female member such that the outwardly extending splines of the male member cooperate with the inwardly extending splines of the female member. As a result, the male and female members are connected together for concurrent rotational movement. However, the outwardly extending splines of the male member can slide relative to the inwardly extending splines of the female member to allow a limited amount of relative axial movement to occur between the engine/transmission assembly and the axle assembly of the drive train system.
Frequently, the cooperating splines of the male and female splined members are disposed within a lubricant chamber that is defined between a pair of sealing structures provided on the slip joint. To accomplish this, the slip joint typically includes both an external sealing structure and an internal sealing structure. The exterior sealing structure is usually supported on the outer surface of the female splined member and extends inwardly into sliding and sealing engagement with the male splined member to prevent contaminants from entering into the region of the cooperating splines from the exterior environment. The interior sealing structure is often supported within the female splined member to prevent contaminants from entering into the region of the cooperating splines from the interior of the female splined member. A variety of such external and internal sealing structures are known in the art. The sealed lubricant chamber is usually filled with a lubricant that not only reduces the amount of sliding friction between the cooperating splines of the male and female splined members, but also substantially fills the volume of the lubricant chamber to further deter the entry of contaminants therein.
Although the use of such external and internal sealing structures has been effective, it has been found that during normal operation of the driveshaft assembly, the axial movement of the male splined member relative to the female splined member causes the volume of the lubricant chamber to vary. Such changes in the volume of the lubricant chamber can, in some instances, result in a pumping action that can discharge lubricant from the lubricant chamber and thereafter create a negative pressure situation within the lubricant chamber (i.e., a situation where the fluid pressure within the lubricant chamber is less than the fluid pressure outside of the lubricant chamber). This negative pressure situation tends to undesirably draw contaminants through either or both of the sealing structures and into the region of the cooperating splines of the male and female splined members. To prevent this from occurring, it is known to form a vent hole through one of the male and female members. The vent hole communicates with the lubricant chamber to prevent this negative pressure situation from occurring. However, the formation of a vent hole has been found to be undesirable for other reasons. Thus, it would be desirable to provide an improved structure for a slip joint that prevents a negative pressure situation from occurring within the lubricant chamber during operation thereof.